Stuck at wp 4.0.8 please help.

Hi there,
As said in the title, I can’t update wp since 4.0.8. Updating breaks the behavior of some pages. The problem occurs since 4.1 and I tracked it down to ‘wp/wp-includes/query.php’.

What happens :
I created a page and assigned a template to it.
The template runs a custom WP_query to get the sticky post from a specific post_type :

$args = array('posts_per_page' => 1, 'post_type' => 'my_CPT', 'post__in' => get_option( 'sticky_posts' ));
$query = new WP_Query( $args );
while ( $query->have_posts() ) : $query->the_post();
…
endwhile;

In wp 4.0.8 ‘the_content()’ returns the full post.
Since wp 4.1 ‘the_content()’ returns only the portion before the ‘more-link’ (needed, used elsewhere on the site).
AFAIK there shouldn’t be any ‘Read more’ link on ‘single’ or ‘page’ unless you call ‘the_excerpt()’.

I tried so many things to fix it but I run out of ideas now.
If you have any clue please help.

Regards,
Fabrice